1. Field of the Invention
The present invention relates to an organic light emitting device formed by organic light emitting elements such as organic electroluminescence elements having emission layers of an organic material and a method of manufacturing the same.
2. Description of the Prior Art
In recent years, an organic electroluminescence element (hereinafter referred to as an organic EL element) having excellent characteristics such as a wide viewing angle, high-speed responsibility, low power consumption and the like is energetically studied. The basic structure of the organic EL element is obtained by forming an organic thin film containing a luminescent material between a transparent electrode (hole injection electrode) of ITO (indium-tin oxide) or the like and a cathode (electron injection electrode) of a material having a small work function. This organic EL element emits light due to recombination of holes and electrons, injected from the transparent electrode and the cathode respectively, in the organic thin film containing the luminescent material (refer to C. W. Tang and S. A. Van Slyke, Applied Physics Letters, Vol. 51, No. 12, pp. 913 to 915, 1987).
In an organic light emitting device employing such organic EL elements, a plurality of data electrodes (hole injection electrodes) of transparent conductive films are arranged on a glass substrate in the form of stripes, and a hole transport layer, an emission layer and an electron transport layer are stacked on the data electrodes, while a plurality of scan electrodes are arranged on the electron transport layer to be perpendicular to the data electrodes. Thus, organic EL elements are formed on the intersections between the plurality of data electrodes and the plurality of scan electrodes, for forming a dot matrix of the plurality of organic EL elements.
Methods of driving such an organic light emitting device formed by a dot matrix of a plurality of organic EL elements can be roughly classified into two systems, i.e., a passive matrix driving system and an active matrix driving system. In the passive matrix driving system, organic EL elements arranged on intersections between a plurality of scan electrodes and a plurality of data electrodes are driven in a time-sharing manner. In the active matrix driving system, organic EL elements are provided on intersections between a plurality of scan electrodes and a plurality of data electrodes through switching elements, to be selectively driven by the switching elements.
FIG. 7 is a schematic plan view showing a conventional organic light emitting device of the passive matrix driving system employing organic EL elements. FIG. 8 is a sectional view of the organic light emitting device taken along the line Dxe2x80x94D in FIG. 7.
As shown in FIGS. 7 and 8, a plurality of striped data electrodes 2 vertically extending along arrow Y are arranged on a transparent substrate 1 of glass. Each of FIGS. 7 and 8 illustrates only three data electrodes 2. The data electrodes 2 are formed by transparent conductive films of ITO (indium-tin oxide) or the like. Such data electrodes 2 have high electric resistance, and hence vertically extending bus lines 3 are formed on partial regions of the data electrodes 2 or adjacently in contact with the data electrodes 2, in order to ensure conductivity. The bus lines 3 are formed by low-resistance metal films of Cr/Mo/Cr or the like.
An organic thin film 6 including a hole transport layer, an emission layer and an electron transport layer is formed on the data electrodes 2. A plurality of striped scan electrodes 7 horizontally extending along arrow X are arranged on the organic thin film 6 to be perpendicular to the data electrodes 2. Organic EL elements are formed on intersections where the data electrodes 2 and the scan electrodes 7 oppositely intersect with each other. Each organic EL element forms a single pixel. Barrier layers 8 of a photoresist material are provided between the plurality of scan electrodes 7. Thus, the plurality of scan electrodes 7 are isolated from each other.
The aforementioned organic light emitting device of the passive matrix driving system can advantageously be more readily manufactured at a lower cost as compared with an organic light emitting device of the active matrix driving system having a plurality of switching elements arranged on a substrate.
In order to drive the organic light emitting device of the passive matrix driving system, a voltage is successively applied to the plurality of scan electrodes 7 in one frame. Thus, a row of pixels located under each scan electrode 7 are selected so that each pixel enters a luminous state or a non-luminous state in response to a voltage applied to the data electrodes 2.
The organic light emitting device of the passive matrix driving system is desired to be improved in luminance and definition and increased in size, to be capable of displaying continuous motion pictures.
In order to improve the definition and increase the size of the organic light emitting device, the number of the scan electrodes 7 must be increased. When the number of the scan electrodes 7 is increased, however, the number of the rows of the pixels successively selected in one frame is so increased that the selection time for each pixel is reduced to reduce the duty ratio. The term xe2x80x9cduty ratioxe2x80x9d stands for the ratio of the time when each pixel is selected in one frame. When the duty ratio is reduced, luminance visually recognized by human eyes is reduced.
In order to ensure sufficient luminance in the organic light emitting device, the selected pixels must emit light in high luminance. Therefore, the organic EL element forming each pixel must be driven at a high voltage. In this case, a high electric field is applied to each organic EL element, to increase the temperature. When an organic EL element is left under a high electric field and a high temperature in general, deterioration of the organic material rapidly progresses to remarkably reduce reliability of the element. Therefore, it is difficult to improve the luminance and definition and increase the size of the organic light emitting device while ensuring the reliability.
As hereinabove described, a technique of providing the barrier layers 8 between the scan electrodes 7 by patterning a photoresist material is employed for isolating the plurality of scan electrodes 7 from each other. However, the aperture ratio (the ratio of the pixel region to a display region) of the pixels is remarkably reduced due to the barrier layers 8 inserted between the scan electrodes 7. In order to compensate for such reduction of the aperture ratio of the pixels, each pixel must emit light in high luminance. Thus, the reliability of the element is remarkably reduced as described above.
When the barrier layers 8 of a photoresist material are formed between the plurality of scan electrodes 7, the photoresist material must be patterned into an optimum shape. However, the photoresist material is generally patterned through a wet process, and hence it is difficult to pattern the photoresist material into a precise shape due to residues etc. resulting from the patterning. Consequently, the non-defective ratio of the organic light emitting device is reduced.
Further, the barrier layers 8 of a photoresist material contain a larger amount of moisture as compared with the data electrodes 2, the organic thin film 6 and the scan electrodes 7. This moisture may gradually permeate into the scan electrodes 7, to oxidize a metal. Thus, current injection efficiency is extremely reduced, to result in dark spots. Or, the moisture permeating from the barrier layers 8 may inactivate the interface between the organic thin film 6 and the scan electrodes 7. Also in this case, light emitting potions are gradually contracted, to result in dark spots. Such permeation of the moisture into the interface between the organic thin film 6 and the scan electrodes 7 progresses from both ends of the scan electrodes 7 isolated from each other by the barrier layers 8. Thus, the number of portions invaded by the moisture is increased as the number of the scan electrodes 7 is increased, to accelerate deterioration of element characteristics.
An object of the present invention is to provide an organic light emitting device having high reliability, which can be improved in luminance and definition and increased size, and a method of manufacturing the same.
An organic light emitting device according to an aspect of the present invention comprises a substrate, a plurality of first electrode layers formed on the substrate along a first direction, an insulating layer formed to cover upper portions of the plurality of first electrode layers and clearances between the plurality of first electrode layers and having a plurality of openings on the plurality of first electrode layers, a plurality of second electrode layers arranged on the insulating layer in the form of a matrix to be electrically connected to the plurality of fist electrode layers through the plurality of openings, an organic thin film, formed on the plurality of second electrode layers, including an emission layer, and a plurality of third electrode layers formed on the organic thin film along a second direction intersecting with the first direction, wherein the plurality of first electrode layers are divided into units each including m (m: at least two) adjacent first electrode layers, a plurality of second electrode layers located above the m first electrode layers of each unit are divided into units each including m second electrode layers arranged to deviate in the first direction and adjacent to each other, the m second electrode layers of each unit are connected to the m first electrode layers of the corresponding unit through the openings of the insulating layer respectively, and each third electrode layer has a width covering a portion above the m second electrode layers of each unit in the first direction.
In this organic light emitting device, the second electrode layers located on the intersections between the first electrode layers and the third electrode layers, the organic thin film including the emission layer and the third electrode layers form organic light emitting elements. The organic light emitting elements form pixels.
The m second electrode layers of each unit are arranged to deviate in the first direction and each third electrode layer has a width covering the portion above the m second electrode layers of each unit, whereby the pixels are arranged under each third electrode layer in a plurality of rows. Therefore, a plurality of rows of elements are simultaneously selected by each third electrode layer. Thus, the number of the third electrode layers can be reduced.
If the number of the third electrode layers is reduced, the ratio of the time for selecting each pixel in one frame can be increased when the plurality of third electrode layers are successively driven in one frame. Consequently, luminance can be improved without driving the organic light emitting element forming each pixel at a high voltage. Therefore, the organic material is prevented from deterioration caused by application of a high electric field and heat generation, and reliability of the organic light emitting device is improved.
When the number of the third electrode layers is reduced, further, the regions between the third electrode layers are also reduced, whereby the ratio of the pixel region to a display region can be increased. Thus, high luminance can be attained. Further, moisture is inhibited from permeating into the organic thin film from the regions between the third electrode layers, due to the reduction of the regions between the third electrode layers. Thus, the organic light emitting elements are prevented from deterioration of characteristics.
When the number of the third electrode layers is reduced, in addition, patterning accuracy for barrier layers formed between the third electrode layers is relaxed. Thus, the non-defective ratio of the organic light emitting device is improved.
On the other hand, it is also possible to increase the number of the third electrode layers thereby increasing the number of rows of the pixels while ensuring prescribed luminance. Consequently, the organic light emitting device can be improved in definition and increased in size without driving the organic light emitting element forming each element at a high voltage. Therefore, the organic material is prevented from deterioration caused by application of a high electric field and heat generation, and the reliability of the organic light emitting device is ensured.
The plurality of first electrode layers are covered with the insulating layer, whereby electric shorting hardly takes place across the first electrode layers and the third electrode layers arranged to intersect with each other. Thus, the organic light emitting device is improved in reliability.
Each of the plurality of second electrode layers may have a larger area than the openings provided in the insulating layer. In this case, the area of each pixel can be increased, whereby the organic light emitting device can be further improved in luminance and definition.
Each of the m second electrode layers of each unit may have a length covering a portion above the m first electrode layers of the corresponding unit in the second direction.
In this case, the area of each pixel is so increased that the ratio of the pixel region to the display region is increased. Thus, the organic light emitting device can be further improved in luminance and definition.
The insulating layer may be made of an oxide, a nitride, a carbide, a sulfide or a polymer film. Permeation of moisture can be sufficiently prevented particularly when the insulating layer is made of an oxide, a nitride, a carbide or a sulfide.
The organic light emitting device may further comprise a plurality of bus lines formed on the plurality of first electrode layers respectively. Thus, the first electrode layers are improved in conductivity.
An organic light emitting device according to another aspect of the present invention comprises a substrate, a plurality of first electrode layers formed on the substrate along a first direction, an insulating layer formed to cover upper portions of the plurality of first electrode layers and clearances between the plurality of first electrode layers and having a plurality of openings on the plurality of first electrode layers, a plurality of second electrode layers arranged on the insulating layer in the form of a matrix to be electrically connected to the plurality of first electrode layers through the plurality of openings, an organic thin film, formed on the plurality of second electrode layers, including an emission layer, and a plurality of third electrode layers formed on the organic thin film along a second direction intersecting with the first direction.
In this organic light emitting device, the second electrode layers located on the intersections between the first electrode layers and the third electrode layers, the organic thin film including the emission layer and the third electrode layers form organic light emitting elements. The organic light emitting elements form pixels.
In particular, the plurality of first electrode layers are covered with the insulating layer, whereby electrical shorting hardly takes place across the first electrode layers and the third electrode layers arranged to intersect with each other. Therefore, the organic light emitting device is improved in reliability.
Each of the plurality of second electrode layers may have a lager area than the openings provided in the insulating layer. In this case, the area of each pixel can be increased, whereby the organic light emitting device can be further improved in luminance and definition.
The insulating layer may be made of an oxide, a nitride, a carbide, a sulfide or a polymer film. Permeation of moisture can be sufficiently prevented particularly when the insulating layer is made of an oxide, a nitride, a carbide or a sulfide.
The organic light emitting device may further comprise a plurality of bus lines formed on the plurality of first electrode layers respectively. Thus, the first electrode layers are improved in conductivity.
A method of manufacturing an organic light emitting device according to still another aspect of the present invention comprises steps of forming a plurality of first electrode layers on a substrate along a first direction, forming an insulating layer to cover upper portions of the plurality of first electrode layers and clearances between the plurality of first electrode layers, forming a plurality of openings in the insulating layer located on the plurality of first electrode layers, forming a plurality of second electrode layers on the insulating layer in the form of a matrix to be electrically connected to the plurality of first electrode layers through the plurality of openings, forming an organic thin film including an emission layer on the plurality of second electrode layers, and forming a plurality of third electrode layers on the organic thin film along a second direction intersecting with the first direction, wherein the step of forming a plurality of second electrode layers includes a step of dividing the plurality of first electrode layers into units each including m (m: at least two) adjacent first electrode layers, dividing a plurality of second electrode layers located above the m first electrode layers of each unit into units each including m second electrode layers arranged to deviate in the first direction and adjacent to each other, and connecting the m second electrode layers of each unit to the m first electrode layers of the corresponding unit through the openings of the insulating layer respectively, and the step of forming a plurality of third electrode layers includes a step of forming each third electrode layer in a width covering a portion above the m second electrode layers of each unit in the first direction.
In the organic light emitting device manufactured by the method according to the present invention, the second electrode layers located on the intersections between the first electrode layers and the third electrode layers, the organic thin film including the emission layer and the third electrode layers form organic light emitting elements. The organic light emitting elements form pixels.
The m second electrode layers of each unit are arranged to deviate in the first direction and each third electrode layer has a width covering the portion above the m second electrode layers of each unit, whereby the pixels are arranged in a plurality of rows under each third electrode layer. Thus, a plurality of rows of pixels are simultaneously selected by each third electrode layer. Thus, the number of the third electrode layers can be reduced.
If the number of the third electrode layers is reduced, the ratio of the time for selecting each pixel in one frame can be increased when the plurality of third electrode layers are successively driven in one frame. Consequently, luminance can be improved without driving the organic light emitting element forming each pixel at a high voltage. Therefore, the organic material is prevented from deterioration caused by application of a high electric field and heat generation, and reliability of the organic light emitting device is improved.
When the number of the third electrode layers is reduced, further, the regions between the third electrode layers are also reduced, whereby the ratio of the pixel region to a display region can be increased. Thus, high luminance can be attained. Further, moisture is inhibited from permeating into the organic thin film from the regions between the third electrode layers, due to the reduction of the regions between the third electrode layers. Thus, the organic light emitting elements are prevented from deterioration of characteristics.
When the number of the third electrode layers is reduced, in addition, patterning accuracy for barrier layers formed between the third electrode layers is relaxed. Thus, the non-defective ratio of the organic light emitting device is improved.
On the other hand, it is also possible to increase the number of the third electrode layers thereby increasing the number of rows of the pixels while ensuring prescribed luminance. Consequently, the organic light emitting device can be improved in definition and increased in size without driving the organic light emitting element forming each element at a high voltage. Therefore, the organic material is prevented from deterioration caused by application of a high electric field and heat generation, and the reliability of the organic light emitting device is ensured.
The plurality of first electrode layers are covered with the insulating layer, whereby electric shorting hardly takes place across the first electrode layers and the third electrode layers arranged to intersect with each other. Thus, the organic light emitting device is improved in reliability.
Each of the plurality of second electrode layers may have a larger area than the openings provided in the insulating layer. In this case, the area of each pixel can be increased, whereby the organic light emitting device can be further improved in luminance and definition.
Each of the m second electrode layers of each unit may have a length covering a portion above the m first electrode layers of the corresponding unit in the second direction.
In this case, the area of each pixel is so increased that the ratio of the pixel region to the display region is increased. Thus, the organic light emitting device can be further improved in luminance and definition.
The insulating layer may be made of an oxide, a nitride, a carbide, a sulfide or a polymer film. Permeation of moisture can be sufficiently prevented particularly when the insulating layer is made of an oxide, a nitride, a carbide or a sulfide.
The method of manufacturing an organic light emitting device may further comprise a step of forming a plurality of bus lines on the plurality of first electrode layers respectively. Thus, the first electrode layers are improved in conductivity.
A method of manufacturing an organic light emitting device according to a further aspect of the present invention comprises steps of forming a plurality of first electrode layers on a substrate along a first direction, forming an insulating layer to cover upper portions of the plurality of first electrode layers and clearances between the plurality of first electrode layers, forming a plurality of openings in the insulating layer located on the plurality of first electrode layers, forming a plurality of second electrode layers on the insulating layer in the form of a matrix to be electrically connected to the plurality of first electrode layers through the plurality of openings, forming an organic thin film including an emission layer on the plurality of second electrode layers, and forming a plurality of third electrode layers on the organic thin film along a second direction intersecting with the first direction.
In the organic light emitting device manufactured by this method, the second electrode layers located on the intersections between the first electrode layers and the third electrode layers, the organic thin film including the emission layer and the third electrode layers form organic light emitting elements. The organic light emitting elements form pixels.
In particular, the plurality of first electrode layers are covered with the insulating layer, whereby electric shorting hardly takes place across the first electrode layers and the third electrode layers arranged to intersect with each other. Therefore, the organic light emitting device is improved in reliability.
Each of the plurality of second electrode layers may have a lager area than the openings provided in the insulating layer. In this case, the area of each pixel can be increased, whereby the organic light emitting device can be further improved in luminance and definition.
In this case, the area of each pixel is so increased that the ratio of the pixel region to the display region is increased. Thus, the organic light emitting device can be further improved in luminance and definition.
The insulating layer may be made of an oxide, a nitride, a carbide, a sulfide or a polymer film. Permeation of moisture can be sufficiently prevented particularly when the insulating layer is made of an oxide, a nitride, a carbide or a sulfide.
The method may further comprise a step of forming a plurality of bus lines on the plurality of first electrode layers respectively. Thus, the first electrode layers are improved in conductivity.